In a reciprocating or scroll saw it is standard for the blade to be elongated and to be moved back and forth in a straight line parallel to its longitudinal axis. As described in "Sagenhaft" (WILPU; 1995) such blades are normally intended to cut in one direction. To this end the teeth are generally triangular, with relative to a forward sawing direction a steep front flank and a shallow rear flank, and set so that they cut into the workpiece in only the forward direction, normally while moving upward, and simply slide without cutting when moving oppositely. When such a saw blade is driven by a crank mechanism it is also fairly common for it to move somewhat perpendicular to its longitudinal direction, advancing forward at the start of its cutting stroke and backward slightly before its noncutting return stroke. Otherwise during the return stroke the blade rubs uselessly on the workpiece, heating it while doing no useful work.
While a standard pruning saw has teeth that are basically M-shaped, such a saw cannot cut in both directions. Instead it cuts on the forward stroke but jumps when pulled back. The teeth of such as saw are normally totally planar and not sharpened.